using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(UnixTimeHelper.FromUnixTimestampMilliSeconds(522510192000));

        Console.WriteLine(UnixTimeHelper.FromUnixTimestampMilliSeconds(522509312000));

    }

}

​

public class UnixTimeHelper

    {

        private static readonly DateTime UnixEpoch =

           new DateTime(2000, 1, 1, 0, 0, 0, DateTimeKind.Utc);

​

        public static long GetCurrentUnixTimestampSeconds()

        {

            return ToUnixTimestampSeconds(DateTime.UtcNow);

        }

​

        public static long ToUnixTimestampSeconds(DateTime dateTime)

        {

            return (long)(dateTime - UnixEpoch).TotalSeconds;

        }

​

        public static long ToUnixTimestampMilliseconds(DateTime dateTime)

        {

            return (long)(dateTime - UnixEpoch).TotalMilliseconds;

        }

​

        public static DateTime FromUnixTimestampSeconds(long seconds)

        {

            return UnixEpoch.AddSeconds(seconds);

        }

​

        public static DateTime FromUnixTimestampMilliSeconds(long miliseconds)

        {

            return UnixEpoch.AddMilliseconds(miliseconds);

        }

    }